1. Field of the Invention
The invention relates to internal combustion engines and more particularly to methods and systems for diagnosing proper operability of air or air-fuel mixture, referred to herein as charge, motion control (CMC) devices used in such engines. Still more particularly, the invention relates to cam profile switching mechanisms and swirl control valves used in such engines to provide such charge motion.
2. Background Information
As is known in the art, charge motion control devices (CMCs) are used to provide greater combustion stability over a wider range of operation in internal combustion engines. One such charge motion device is a cam profile (CPS) switching mechanism. For example, cam profile switching is a mechanism by which the cam operating an intake valve of the engine is changed from following a first cam to following a second cam, such change occurring in about one engine revolution. This switching action results in the generation of charge motion in the cylinder.
As is also known in the art, at marginal combustion conditions, e.g., with lean air/fuel mixtures in the cylinder or air/fuel mixture diluted with a large fraction of exhaust gases in the cylinder, it is desirable to have a high air/fuel motion turbulence level to aid in the ignition produced flame propagating through the cylinder. At more robust combustion conditions, such as those that occur at high torque demand, high turbulence causes harsh, noisy combustion in the cylinder due to the flame propagating too fast thereby causing an excessive rate of pressure rise in the cylinder. With a CPS device, the cam can be switched to provide the appropriate charge motion in the cylinder, thereby conforming to the engine operating condition.
The inventors of the present invention have recognized the desirability of confirming that the charge motion control device is operating as expected. Since CPS affects primarily charge delivery, it is natural to attempt to determine CPS integrity based on a charge model. However, the inventors of the present invention have discovered that engineering data show little or no sensitivity in charge data to CPS position at part load.
The inventors of the present invention have observed that when CPS position is changed from one cam to the other, at a constant engine operating condition, engine exhaust temperature changes by 50 to 100 degrees Celsius, depending on engine operating condition. The inventors have discovered that a determination can be made as to whether a charge motion (CMC) device is operating properly by comparing actual exhaust temperature with exhaust temperature expected from operating the engine with the CMC device in a predetermined one of at least two different charge motion generating positions.
The exhaust temperature difference that is noticed when the CMC device is in the other of the positions than is expected is due to the fact that when the electronic control unit commands a first position, the electronic controller also commands spark timing, fuel injection, exhaust gas recirculation quantity, and other parameters assuming that the CMC device has, indeed, assumed the commanded position. If the CMC device is inoperable and is in the other position than that commanded, but the electronic control unit commands the other engine parameters for the appropriate positioning of the CMC device, then the values of the engine parameters are inappropriate for the actual CMC device position, thus, yielding the rather substantial difference in exhaust temperature from that expected, i.e., a 50-100 degree Celsius differential.
The inventors have also discovered that if the CMC device has been found to operating improperly, information about the improper operation can also be assessed. By comparing both measured exhaust temperatures and expected temperatures with the CMC commanded to be in a first one of the positions and then with the CMC commanded to be in the other position, such an assessment can be made.
The inventors disclose a method for detecting a proper operability in a charge motion control device in an internal combustion engine, the charge motion control device being capable of assuming one of at least two positions. The method includes commanding the charge motion control device to assume one of the two positions. The method determines a measured exhaust temperature, Tm1. The method also determines a first expected exhaust temperature, Ts1, based on a present engine operating condition and the position commanded to the charge motion control device. The method provides detection of improper operability in response to the measured temperature and said first expected exhaust temperature. Further, a second expected exhaust temperature, Ts2, based on a present engine operating condition and the charge motion control device being in the other of the two positions is determined. The improper operability is detected based also on the second expected exhaust temperature. Additionally, the charge motion control device is commanded to assume such other position. A second measured exhaust temperature, Tm2, is measured in response to commanding the charge motion control device to be in the other position. The improper operability detection is further based on Tm2.
The inventors also disclose a system for detecting an improper operating charge motion control device disposed in an internal combustion engine. The charge motion control device is capable of assuming a first position and a second position. The system includes a temperature sensor disposed in an engine exhaust and an electronic control unit operably coupled to the charge motion control device, the engine, and the temperature sensor. The electronic control unit commands the charge motion control device to assume the first position. The electronic control unit determines a first expected exhaust temperature, Ts1, based on a present engine operating condition and the charge motion control device being in the first position. The electronic control unit detects the improper operation based on the first expected exhaust temperature and a measured temperature, Tm1, determined from the temperature sensor. The electronic control unit determines a second expected exhaust temperature, Ts2, based on the present engine operating condition and the charge motion control device being in the second position and bases the improper operation detection further on Ts2.
The present invention provides a robust method for detecting improper operation of a charge motion control device based on a signal from a temperature sensor in the engine exhaust.
Another advantage of the present invention is that it provides differentiation between a dislocated and a stuck charge motion control device. A stuck device is one that is stuck in an unknown position, i.e., could be in the first position, the second position or any position in between. A dislocated device is one that is in the second position when it is commanded to the first position or vice versa.
Another advantage of the invention is that the method provides several levels of error checking provided to prevent a false indication that an error has occurred.